IIS on win 2003 server, filtered port 80

I'm running IIS on win 2003 server (sp1) here on my LAN. Port 80
seems to be getting blocked.

As long as the IIS website port is set to anything but 80 it works
fine. I have used 81 and 8080 no problem.

I have checked and the firewall is off.

The TCP/IP Filtering in the network adaptor is off

There is no other firewall software installed.

an nmap from one of our linux servers declares that "80/tcp filtered
http" port 80 is filtered as opposed to our linux webserver which it
finds as open on 80 as expected.

I've tried adding another IP to the card so that it has x.x.x.14 and
x.x.x.15 but no change on the new IP.

All traffic across my LAN so it isn't an ISP filter and we're not
running any hardware firewalls on our LAN

Anyone got any other clues on what to poke at?

Thanks!
Craig

oops sorry for the double post.